Photochemistry has become an important area to consider in the semiconductor fabrication process. The role of Photochemistry is expanding from diverse areas of biology and medicine to semiconductor processing. Due to chemical reactions involved in several semiconductor fabrication steps, the quality of the reactions can be controlled by selective use of photochemistry in general and photons in particular. The raw materials in Ultra Large Scale Integration (USLI) electronics involve thermal processing which can provide defect free engineering of a desired thin film.
As an example, for the deposition of superconducting thin films, rapid thermal processing (RTP) assisted metalorganic chemical vapor deposition (MOCVD) has provided encouraging process results using lower deposition temperatures. Although the decomposition pathways of most of the reactions are not accurately known, in general, most of the organometallics used in MOCVD have higher adsorption coefficients in ultraviolet (UV) and vacuum ultraviolet (VUV) regions. High energy photons, from the UV and VUV regions, provide excited but not dissociated complexes. Thus, in concert with the low energy photons (responsible for the thermal or pyrolysis deposition), the high energy photons can provide the ideal MOCVD approach for the growth of many materials.
A photochemical reaction is a chemical reaction which takes place only under the influence of light. For the purposes of Photochemistry, light is considered as being made up of individual photons of energy E=hv, where h is Planck's constant and v is the frequency of light Only light that is absorbed can result in a photochemical effect. On the molecular scale the photochemical reaction starts with the adsorption of a photon by a molecule. The molecule is thereby promoted to an excited state. The excited molecule is a new chemical species which has its own distinct chemical and physical properties.
Any photochemical event starts with the absorption of a photon by a molecule M, with production of an excited molecule M*, where M+hv=M* (adsorption). The excited molecule M* may now react chemically, either by rearrangement or, for instance, by reaction with another species N: M*+N=P. This step which involves, chemically, the excited molecule M*, is the primary photochemical process.
Another type of molecular excitation is rotational excitation which requires the smallest amount of energy. Rotational excitation results in a spinning of the molecule around a preferred axis. The molecule is however chemically unchanged With higher energies the molecule can be promoted to a vibrationally excited state. Here again the molecule is chemically unchanged as the energy is in the form of vibrations of various parts of the molecule. With even higher energies, the molecule will be electronically excited as one or several electrons are promoted to higher energy orbitals. Photochemical reactions occur from such electronically excited state of molecules.
The ground state of the atom is the state in which all the electrons fill the available orbitals in the order of increasing energy. An electronically excited state is a state in which one or several electrons occupy higher energy orbitals, having left one or several vacancies in the lower orbitals. A ground state can only adsorb light, it cannot emit light. An excited state can either emit light (thus moving downwards in energy to the ground state or to a lower excited state) or absorb light (thus moving upwards in energy to a higher excited state).
In literature it is also known that an VUV lamp greatly improves the quality of dielectric films, such as Y.sub.2 O.sub.3 films and superconducting films (YBCO complexes) due to the use of higher energy photons in the deposition process. The heating source configuration plays an important role in film deposition, which is very useful in the optimization of lamp energy source design. The leakage current density of dielectric films is good enough to replace conventional oxides as the insulator in the devices processing. Quality films can be grown at low substrate temperature by using VUV lamps as the source of optical energy.
The present invention provides an apparatus and method for commercial semiconductor fabrication that uses the combination of UV lamps and infrared radiation sources to form and condition films, such as dielectric films.